Surface fluxes of momentum and mechanical energy over the North Pacific and North Atlantic Oceans |
| |
Authors: | I Simmonds K Keay |
| |
Institution: | (1) School of Earth Sciences, University of Melbourne, Australia, AU |
| |
Abstract: | Summary Using 6-hourly data from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis
set (1958–1997) we have determined the winter and summer mean fluxes of momentum and mechanical energy into the Northern Hemisphere
(NH) oceans. We have also diagnosed the contribution made to these by the mean wind speed and the covariances due to the temporal
variability. In both seasons the greatest oceanic flux of momentum is found in the region to the south of Greenland and Iceland.
The contributions to the total made by the transient term exhibited maxima in the north central Pacific and Atlantic and in
winter, and accounts for about 15% of the mean stress in both extratropical ocean basins and both seasons. The rate at which
mechanical energy is imparted to the ocean shows a similar spatial structure. The fluxes are typically three times larger
in winter, and about one third of the input is associated with the transient part of the low level wind. The spatial and temporal
structure of the part of fluxes contributed by the temporal variability shows a strong relationship with mean cyclone depth,
a parameter known to represent an unbiased measure of cyclone activity.
The fluxes exhibit significant positive winter trends (many of which are significant) over the extratropical Pacific and in
the Atlantic north of about 40° N, and these have been found to result from reinforcing trends in the components associated
with the mean wind speed and the temporally varying part. The changes are broadly in line with those in observed significant
wave height over the northern oceans in recent decades, and are closely related to secular increases in the mean depth of
cyclones. Positive trends in the number of extreme cyclones in key regions of the Pacific and Atlantic have been found. The
trend is significant in the relevant part of the Pacific, but whether the increase in the Atlantic subregion should be regarded
as above the noise is seen to depend on how such extremes are defined. We discuss how conclusions drawn in specific studies
may depend critically on how cyclones and extreme events are characterized.
Received November 2, 2001 Revised December 24, 2001 |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|